This invention relates to azeotrope-like or essentially constant-boiling mixtures of pentafluoropropane and a perfluorinated fluorocarbon having 5 to 7 carbon atoms or N-methylperfluoromorpholine or N-ethylperfluoromorpholine. These mixtures are useful as refrigerants for heating and cooling.
Fluorocarbon based fluids have found widespread use in industry for refrigeration applications such as air conditioning and heat pump applications.
Vapor compression is one type of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because for heating, the operation of the condenser is inter-changed with that of the refrigeration evaporator.
Certain chlorofluoromethane and chlorofluoroethane derivatives have gained widespread use in refrigeration applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties. The majority of refrigerants utilized in vapor compression systems are either single components fluids or azeotropic mixtures. Moreover, certain applications, such as centrifugal chillers, can only use pure or azeotropic refrigerants, since non-azeotropic mixtures will separate in pool boiling evaporators, causing undesirable performance.
Azeotropic or azeotrope-like compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor compression equipment with which these refrigerants are employed, condensed material is generated in preparation for cooling or for heating purposes. Unless the refrigerant composition exhibits a constant boiling point, i.e. is azeotrope-like, fractionation and segregation will occur upon evaporation and condensation and undesirable refrigerant distribution may act to upset the cooling or heating. If a leak occurs in a refrigeration system during use or service the composition of the azeotrope-like mixture does not change and thus, system pressures and system performance remain unaffected.
The art is continually seeking new fluorocarbon based azeotrope-like mixtures which offer alternatives for refrigeration and heat pump applications. Currently, of particular interest, are fluorocarbon based azeotrope-like mixtures which are considered to be environmentally safe substitutes for the presently used fully halogenated chlorofluorocarbons (CFC""s), such as trichlorofluoromethane (R-11), which are suspected of causing environmental problems in connection with the earth""s protective ozone layer.
The substitute materials must also possess those properties unique to the CFC""s including chemical stability, low toxicity, non-flammability, and efficiency in-use. The latter characteristic is important in refrigeration and air-conditioning especially where a loss in refrigerant thermodynamic performance or energyefficiency may have secondary environmental impacts through increase fossil fuel usage arising from an increased demand for electrical energy. Furthermore, the ideal CFC refrigerant substitute would not require major engineering changes to conventional vapor compression technology currently used with CFC refrigerants.
Mathematical models have substantiated that hydro-fluorocarbons, such as pentafluoropropane, including 1,1,2,2,3-pentafluoropropane (HFC-245ca), 1,1,2,3,3-pentafluoropropane (HFC-245ea), 1,1,1,2,3-pentafluoropropane (HFC-245eb) and 1,1,1,3,3,-pentafluoropropane (HFC-245fa) will not adversely affect atmospheric chemistry, because they are a negligible contributor to ozone depletion and to green-house global warming in comparison to the fully halogenated species.
However, HFC-245eb has been found to have flame limits under normal ambient conditions, and HFC-245ca has been found to have flame limits under humid conditions, but not under dry conditions. It has not been confirmed whether or not other pentafluoropropane isomers also exhibit some finite flame propagation behavior in specific, but yet undetermined, environments. This flame propagation behavior would significantly limit the potential use of the pentafluoropropane isomer as an R-11 replacement in chiller applications.
In accordance with the present invention, novel mixtures have been discovered comprising pentafluoropropane and a perfluorocarbon having 5 to 7 carbon atoms or N-methylperfluoromorpholine or N-ethylperfluoromorpholine. Also, novel azeotrope-like compositions have been discovered comprising pentafluoropropane and a perfluorocarbon selected from the group consisting of perfluoropentane, perfluorohexane and perfluoroheptane or N-methylperfluoromorpholine or N-ethylperfluoromorpholine.
Preferably, the novel azeotrope-like compositions comprise effective amounts of pentafluoropropane and a perfluorocarbon having 5 to 7 carbon atoms or N-methylperfluoromorpholine or N-ethylperfluoromorpholine. The term xe2x80x9ceffective amountsxe2x80x9d as used herein means the amount of each component which upon combination with the other component, results in the formation of the present azeotrope-like compositions.
The preferred, more preferred and most preferred embodiments for each azeotrope-like composition of the invention are set forth in Table I below. The numerical ranges, boiling point and pressures are understood to be prefaced by xe2x80x9caboutxe2x80x9d.
All compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below.
The precise azeotropic compositions have not been determined but have been ascertained to be within the above ranges. Regardless of where the true azeotropes lie, all compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below.
Moreover, these compositions were determined to be nonflammable in air at ambient conditions using the ASTM E-681 method as specified in the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 34-1992.
Because the present novel compositions exhibit essentially constant-vapor pressure characteristics as the liquid mixture is evaporated and show relatively minor shifts in composition during evaporation, the present compositions are advantageous in a vapor compression cycle as they mimic the performance of a constant-boiling single component or azeotropic mixture refrigerant.
From fundamental principles, the thermodynamic state of a fluid is defined by four variables: pressure, temperature, liquid composition and vapor composition, or P-T-X-Y, respectively. An azeotrope is a unique characteristic of a system of two or more components where X and Y are equal at the state P and T. In practice, this means that the components of a mixture cannot be separated during a phase change, and therefore are useful in the cooling and heating applications as described above.
For the purpose of this discussion, azeotrope-like composition is intended to mean that the composition behaves like an azeotrope, i.e. has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation. Thus, in such compositions, the composition of the vapor formed during boiling or evaporation is identical or substantially identical to the original liquid composition. Hence, during boiling or evaporation, the liquid composition, if it changes at all, changes only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which during boiling or evaporation, the liquid composition changes to a substantial degree.
It should be understood that the azeotrope-like compositions of the present invention may include additional components which do not form new azeotropic or azeotrope-like systems i.e., additional components which are not present in a first distillation cut taken as described below.
One way to determine whether the addition of a component forms a new azeotropic or azeotrope-like system so as to be outside of this invention, is to distill a sample thereof under conditions (i.e. resolutionxe2x80x94number of plates) which would be expected to separate the mixture into its separate components. If the mixture containing the additional component is non-azeotropic or non-azeotrope-like, the additional component will fractionate, i.e. separate from the azeotropic or azeotrope-like components. If the mixture is azeotrope-like, some finite amount of a first distillation cut will be obtained which contains all of the mixture components and which is constant-boiling or behaves as a single substance. As used here, the term xe2x80x9cfirst distillation cutxe2x80x9d means the first cut taken after the distillation column displays steady state operation under total reflux conditions.
It follows from the above that another characteristic of azeotrope-like compositions is that there is a range of compositions containing the same components in varying proportions which are azeotrope-like or constant-boiling. All such compositions are intended to be covered by the terms xe2x80x9cazeotrope-likexe2x80x9d or xe2x80x9cconstant-boilingxe2x80x9d as used herein. As an example, it is well known that at differing pressures, the composition of a given azeotrope will vary at least slightly as does the boiling point of the composition. Thus, an azeotrope of A and B represents a unique type of relationship but with a variable composition depending on temperature and/or pressure. As is readily understood by persons skilled in the art, the boiling point of the azeotrope will vary with the pressure.
As such, the present invention meets the need in the art for a refrigerant which has a low ozone depletion potential and is a negligible contributor to green-house global warming compared with fully halogenated CFC refrigerants, is nonflammable, has a COP and capacity comparable to that of R-11, and has a low compressor discharge temperature.
In one process embodiment of the invention, the azeotrope-like compositions of the invention may be used in a method for producing refrigeration which comprises condensing a refrigerant comprising the azeotrope-like compositions and thereafter evaporating the refrigerant in the vicinity of a body to be cooled.
Alternatively, the azeotrope-like compositions of the invention may be used in a method for producing heating which comprises condensing a refrigerant comprising the azeotrope-like compositions in the vicinity of a body to be heated and thereafter evaporating the refrigerant.
The azeotrope-like compositions of the present invention may also be used as heat transfer fluids. For example, in certain refrigeration systems it is desirable to operate the system at a specific temperature. However, maintaining the desired temperature may require either the addition or removal of heat. Thus a secondary heating loop containing an appropriate heat transfer fluid may be added. The heat transfer fluid absorbs heat in one part of the cycle and transfers the heat to another part of the cycle without changing state (when the heat transferred is sensible heat) or by changing state (when the heat transferred is latent heat).
In another process embodiment, the azeotrope-like compositions of the present invention are used in a method for producing polyurethane and polyisocyanurate foams. The method comprises reacting and foaming a mixture of ingredients which forms the polyurethane and polyisocyanurate foams in the presence of a volatile blowing agent comprising the azeotrope-like compositions of the present invention. Alternatively, the azeotrope-like compositions of the present invention are used in a premix of polyol and blowing agent. The premix comprises the azeotrope-like compositions of the present invention prior to reaction and foaming of the ingredients forming polyurethane and polyisocyanurate foams. The blowing agents of the present invention are used alone or in a premix with a polyol. Suitable polyols are generally known in the art, as are disclosed for example in U.S. Pat. No. 5,130,345, which is incorporated by reference.
In still other process embodiments, the azeotrope-like compositions of the present invention may be used in a method for producing foam comprising blending a heat plasticised resin with a volatile blowing agent comprising the azeotrope-like compositions of the present invention 1 and introducing the resin/volatile blowing agent blend into a zone of lower pressure to cause foaming.
The azeotrope-like compositions of the present invention may also be used in a method of dissolving contaminants or removing contaminants from the surface of a substrate. This use comprises the step of contacting the substrate with the azeotrope-like compositions of the present invention. The compositions of the present invention may also be used as fire extinguishing agents.
HFC-245ca, HFC-245ea, HFC-245eb, HFC-245fa, perfluoropentane, perfluorohexane, perfluoroheptane, N-methylperfluoromorpholine or N-ethylperfluoromorpholine are each known materials. Preferably, the materials should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the cooling or heating properties or constant-boiling or the system.
Additional components may be added to the mixture to tailor the properties of the mixture according to the need. For example, in the art, propane has been added to refrigerant compositions to aid oil solubility and may be added to the azeotrope-like compositions of the present invention. Similar materials may be added to the present compositions.
It is also possible to produce thermoplastic foams using the compositions of this invention. For example, conventional foam polyurethanes and isocyanurates formulations are combined with the azeotrope in a conventional manner to produce rigid foams.